In general, the major factors that have been recognized as influencing the likelihood of invasive fungal infection are the patient's immune status, the degree of any organ damage (e.g., mucositis), and overall microbial exposure (i.e., colonization, environment, and prior infection). Since the 1990s, different risk-stratification strategies have been evaluated in order to identify those patients who may benefit from intensive prophylactic and diagnostic measures. However, despite having similar risk profiles, only a subset of AML patients will develop an IFI. One of the most exciting recent advances in the understanding of the epidemiology of IFIs is the recognition of the complexity of the host and the identification of new host-related risk factors.